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ENGIN 112 Homework 6 Please submit your answers on Gradescope via the course page on Canvas You can write your answers electronically or by hand and submit a scan or photo Question 1 Assume you make a phone call between two telephones that are connected to the telephone network via the Internet using a VoIP adapter for each phone Each phone uses a regular U S phone number a Show an illustration that shows what that connection looks like You may show the Internet and the phone network as a cloud i e no internal details required b The voice information for this phone call can be carried in three forms analog digital in the phone network and digital on the Internet State the order in which form the voice information for this call is transferred Analog original voice input at the phone Digital on the Internet after VoIP conversion Digital in the phone network after entering the telephone network Digital on the Internet return path Digital to analog conversion for phone B Question 2 Answer the following questions about frequency allocations a Download the U S Frequency AllocaNon Chart hVps www nNa doc gov files nNa publicaNons january 2016 spectrum wall chart pdf Identify a frequency range used for cellular telephony in the chart e g 809MHz 849MHz What is the label for this frequency range in the chart 854 0 MHz to 894 0 MHz is used for cellular telephony in the chart The label for this frequency range is Land Mobile b Consider the frequency allocation for the United Kingdom http www onlineconversion com downloads uk frequency allocations chart pdf What would you perceive as a challenge when building cell phone infrastructure that crosses national boundaries 2 3 sentences 52 0 MHz to 68 0 MHz is one of the frequencies ranges used for cellular telephony in the United Kingdom A key challenge when building cell phone infrastructure across national boundaries is that different countries may allocate different frequency ranges for cellular communications This means that phones and cell towers need to be capable of operating on multiple frequency bands to work across borders increasing complexity and cost of the equipment Question 3 Assume you have two oscillators that generate a carrier signal at 800 MHz 80 ppm Assume that at Nme t 0 both oscillators are synchronized Also assume the worst case difference in frequency between the oscillators i e one oscillating as slow as possible within specification and the other oscillating as fast as possible within specification a At what Nme are the two oscillators exactly opposite to each other i e 180 degrees out of phase You can calculate this Nme by assuming that the slower oscillator will have completed x cycles at that Nme and the faster oscillator will have completed x cycles 800 MHz 800 000 000 Hz 80 ppm 80x10 6 Frequency difference 800 000 000 2 80 10 6 128 Hz Time 0 5 128 0 0039 seconds or 3 9 milliseconds b Assume that you transmit 640 kilobits of binary data per second on this carrier signal Also assume that the data can be received correctly by the receiver when the phase difference between the sender and the receiver is between 0 degrees and 90 degrees How many bits can be transmitted correctly before the sender and receiver are out of sync by more than 90 degrees Phase difference must stay within 90 deg Time until 90deg phase difference 0 0039 2 0 00195 seconds At 640 kbps number of bits 0 00195 640 000 1 248 bits Question 4 10011110 Please answer the following questions regarding the modulation of bits on signal transmission Assuming frequency shift keying higher frequency indicating a 1 what bit sequence is encoded in the following transmission pattern You may assume that 3 oscillations of the lower frequency are transmitted per bit or 6 oscillations of the higher frequency per bit a How is the bit sequence 0111011011 encoded with on off keying In on off keying when the bit is 0 there is no signal and when the bit is 1 there is a signal b What problem do you foresee if you were to transmit 100 000 consecutive bits of value 0 zero using on off keying Would this problem go away if you were to use amplitude shift keying or frequency shift keying The problem with transmitting 100 000 consecutive bits of value 0 using on off keying would be that there is no way of counting the number of no signals or 0 bits that are being transmitted Whereas with frequency shift keying a change in frequency would be detected even if a signal wasn t sent Question 5 Consider the Hamming 7 4 code discussed in the lecture a What is the 7 bit encoding of 0010 when using this code b What is the 7 bit encoding of 0000 when using this code c What is the Hamming distance between 7 bit code words from a and b 0101010 0000000 0010011 0000000 Hamming Distance 3 d Noting that 0010 and 0000 differ by only 1 bit and considering your answer to c explain why a 1 bit transmission error can be corrected with a Hamming 7 4 code A 1 bit transmission error can be corrected because the Hamming 7 4 code has a minimum Hamming distance of 3 This means it can detect which single bit if any has flipped allowing the receiver to pinpoint the error and correct it Assume an 850 MHz electromagnetic signal arrives at a receiver via two paths that Question 6 corresponds to that of light in a vacuum a What is the wavelength of this signal differ in length by a distance of d 10m Assume a propagation speed that 3 108 850 106 0 353 103 108 33 3 0 353 178 2 2 10 2 signal that arrives later c What is the phase difference between the signal that arrives first and the b How much later does the signal along the longer path arrive at the receiver


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UMass Amherst ENGIN 112 - Homework 6

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